The short answer
What Causes the Leak
High-efficiency furnaces condense water vapor from combustion gases, creating acidic water that must drain away. If the drain line, condensate trap, or drain pan is clogged or cracked, that water escapes and pools near the furnace. A humidifier attached to the furnace can also overflow if the float valve sticks or the supply line leaks.
In winter, the temperature difference between the warm furnace area and cold outdoor vents increases condensation. Ice can form in the exhaust or drain pipe, blocking the flow and forcing water back into the unit. Check the drain line for ice or debris, and inspect the pan for rust or cracks that allow water to escape.
- Clogged condensate drain line
- Cracked or rusted drain pan
- Faulty humidifier float valve
- Ice blockage in exhaust or drain pipe
- Loose or damaged drain hose
- High humidity in the furnace room
Check the Condensate Drain First
Start by locating the condensate drain, usually a small tube or hose near the bottom of the furnace. Remove any visible debris, and flush the line with water to clear blockages. If the drain is frozen, gently warm it with a hair dryer; never use an open flame.
Inspect the drain pan for cracks or corrosion. A pan with a small hole can leak slowly and cause water damage over time. If the pan is damaged, the pros often replace it as part of a furnace service. For now, place a shallow container under the leak to catch water and prevent it from reaching flooring or drywall.
Inspect the Humidifier System
If your furnace has a humidifier, check the water supply line and the float valve. A stuck float can let water overflow the reservoir, creating a leak that appears near the furnace. Turn off the water supply to the humidifier and observe if the leaking stops.
Clean the float and valve, and ensure the reservoir is level. If the humidifier is old or cracked, it may need replacement. A plumber can handle the water supply connections, while a water damage pro can clean up any water that has already soaked into surrounding materials.
When to Call the Pros
If you cannot find the source of the leak, or if water has spread to walls, flooring, or the ceiling below, call a local water damage pro. They can use leak detection equipment to trace the water's path and identify hidden damage. Water that sits in drywall or subflooring can lead to mold and structural issues.
Before the pros get to work, turn off the furnace if the leak is severe, and shut off the water supply to the humidifier if it is involved. Move belongings away from the area and remove any wet rugs or cardboard. The pros will typically extract standing water, dry the affected materials, and help you decide what needs repair or replacement.
Prevent Future Winter Leaks
Regular furnace maintenance before winter can prevent many leaks. Have a heating professional clean the condensate trap and drain line annually, and check the humidifier components. Keep the area around the furnace clear so you can spot leaks early.
If you live in a cold climate, keep the area around the furnace clear so you can spot leaks early. Also, consider a water alarm near the furnace to alert you to moisture. If a leak has caused water damage, the pros can help with drying and repairs, including drywall and flooring work.
Water damage does not wait
Water keeps spreading into floors and walls, so it is worth acting early. Calls are answered 24/7.
Call Now (801) 383-0232Frequently asked questions
Is a leaking furnace dangerous?
A small leak is usually not dangerous, but it can damage your home and create mold. The water from a condensing furnace is slightly acidic, so it can corrode metal over time. If the leak is large or near electrical components, turn off the furnace and call a professional.
Can I fix the leak myself?
You can clear a clogged drain line or adjust a humidifier float if you are comfortable. However, if the drain pan is cracked or the heat exchanger is leaking, you need a heating professional. Water damage cleanup is right to leave to the pros to avoid mold and structural issues.
Will my insurance cover furnace water damage?
Policies vary, and your insurer decides what is covered. Water damage from a sudden leak may be covered, but damage from lack of maintenance might not be. Check your policy and document the damage with photos before you contact your insurance company.